Motor switch contact shielding



Dec. 26, 1961 e. F. SEAGREAVES MOTOR SWITCH CONTACT SHIELDING Filed July 13. 1959 IN V EN TOR.

George FSeagreaI/es His A l/orney Unite State This invention relates to dynamoelectric machines and particularly to motor switching shield structure.

An object of this invention is to provide new and improved dust-proof motor switch contact means for use on stationary centrifugal starting switches of dynamoelectric machines.

Another object of this invention is to provide a centrifugal switch mechanism including a pair of starting switch contacts, one of which is movable and secured to an arm so as to help secure an annular metal cover disk to that arm, one end of which is secured for pivotal movement relative to a stationary terminal support of insulating material on which a contact having a head portion is fixed to be in alignment with a path traversed by the movable contact and including a single annular grommet of elastomeric materials open at opposite ends and having first and second annular coaxially-aligned and longitudinally-spaced end portions of differing diameters as well as a laterally extending intermediate portion that establishes radial interconnection between the end portions, that is effective axially in flexing and biasing end portions into sealing engagement peripherally relative to the fixed contact and metal disk around the movable contact, and that provides conjoint action to serve as a seal as well as a spring for biasing the contacts apart while a stop for the movable arm limits separation of the contacts such that the grommet is maintained in assembled relation thereto.

Still another object of this invention is to provide a switch contact assembly with an improvement including a fixed contact on a support of insulating material and a second contact movable into engagement therewith due to displacement of a resilient arm that has attached thereto a cup-shaped cover member of rigid material concentric relative to the movable contact on the arm as well as having a single annular grommet of the clastomeric material having circular openings at opposite ends formed by a relatively larger end portion and a smaller end portion joined to each other at a location intermediate the openings by a laterally extending intermediate portion that establishes coaxial alignment and longitudinal spacing of the end portions, that permits limited telescoping of end portions relative to each other while flexed axially in between the end portions so as to bias end portions into sealing engagement inside the cover member and peripherally outside the contact, and that is maintained under pressure at all times intermediate the contacts for elimination of friction and yet permits easy opening and closing of contacts which are kept cool though protected and isolated from foreign substances such as dirt, oil, dust and grease carried by circulating air currents within a motor housing and which are relatively free of risk of oxidation because atmosphere is restricted and nearly excluded such that fresh supply of oxygen is substantially cut off for minimizing damage due to arcing and sparks relative to the contacts that are maintained in clean and fully-operative condition for a long and indefinite period of time.

atent Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present inventionare clearly shown.

. v In the drawings:

FIGURE 1 is a side view of an end of a dynamoelectric machine having a centrifugal starting switch assembly improved in accordance with the present invention.

FIGURE 2 is a plan view of switch assembly and shielding structure in accordance with the present invention.

FIGURE 3 is a partially exploded perspective view of parts and structure of FIGURES l and 2.

FIGURE 4 is a fragmentary cross-sectional elevational view taken along line 4-4 in FIGURE 2 to show shielding structure and contacts in open position.

FIGURE 4a is similar to FIGURE 4 and shows shielding structure and contacts in closed position.

In FIGURE 1 there is a fragmentary cross-sectional elevational view of an end of a dynamoelectric machine generally indicated by numeral 10 andincluding a stack of stator laminations 10s having slots into which a stator winding 10w is fitted in a well known manner. The dynamoelectric machine also includes a rotor 10r formed out of a stack of laminations relative to which there is provided a squirrel cage winding having an end ring 10c and fan blades 10 integral therewith in a well known manner. The rotor is carried by a shaft S which is journalled in a bearing provided relative to an end cover C suitably attached to an annular housing H into which the stator lamination assembly 103' is fitted in a well known manner. The housing H and end cover Care indicated in FIGURE 1 to facilitate understanding of location of a centrifugal switch mechanism including a speed responsive device generally indicated by numeral 12 and having a tubular sleeve portion 12s slidableaxial- 1y along the shaft S. Sliding movement of the sleeve 12s is effected in response to movement of weight such as 12w pivotally secured relative to the sleeve 12s by means of a bracket 12b. A coil spring such as 12c is provided for biasing the weights 12w in one direction and operation of the speed responsive device and structure thereof can be more fully understood by referring to a patent, 2,747,854, Schnepf, issued May 29, 1956, and belonging to the assignee of'the present invention. 1

The slidable sleeve 12s has an annular face portion 12f engageable relative to a free end 14:; of a resilient arm 14a of a centrifugal switch mechanism generally indicated by numeral 14. The switch mechanism includes a terminal support or bar of insulating material 14b that is suitably mounted relative to the end cover C. The support member 14b has a fixed contact 14:: mounted thereon and formed as a head portion of a threaded terminal 14! visible in FIGURE 1. It is to be understood that suitable threaded nuts can he fitted onto this threaded terminal 142 for establishing connections relative to Wires or terminals on conductors in a well known manner. A washer 14w is fitted between the head portion or fixed contact and the support 14b of insulating material. The stationary or fixed contact 140 is positioned relative to the support member so as to be in alignment with a path of movement of a movable contact member 14m carried by the resilient arm 14a at an intermediate portion thereof. The location of the movable contact 14m relative to the arm 14a can be best seen in FIGURES 1 .and 2. The end 14 of the arm 14a can be attached to projection 14p in any suitable manner such as by brazing or welding whereby a good electrical connection is established between the arm and U-shaped member 1414. It is to be understood that the arm 14a is pivot-able or fulcrumed relative to the end 14) and this pivotable action occurs in response to force exerted by the sleeve member 12s having the face 12 in engagement with the free end 142 of the arm. The U-shaped member 1411 includes a pair of terminal lug portions 14L which project through the support 14b of insulating material as outlined'in FIG- tions or blades of the U-shaped member 1414.

URE 1. These lug portions 14L can be twisted about their longitudinal axis for 30 for example, so as to secure the U-shaped member relative to the support 1412. The lug portions fit through slots 14s provided in the support 14b at predetermined locations. Female terminal means such as disclosed in Patent 2,682,038, Johnson, issued June 22, 1954, and belonging to the assignee of the present invention, can be fitted relative to these lug por- Additional threaded terminals can be mounted relative to the support 14b of insulating material for establishing electrical connections relative to windings w as needed.

The centrifugal switch used as illustrated can make and break electrical connections necessary for operating split-phase and condenser-start single-phase motors, for example. Because the application of a single-phase alternating current to a single stator winding cannot produce a rotating field necessary for developing a starting torque, motors of the above type are generally provided with an auxiliary or starting winding. This starting winding generates a field of flux out of phase with respect to the electromagnetic field of flux of the field or stator Winding such that a resultant flux provides force to produce a starting torque. Once the motor is started, there is set up a rotating field of flux which lags the stator field of flux and which can therefore sustain rotation. When the motor has reached a specified proportion of the ultimate running speed, the energized circuit for a starting Winding is opened by a device such as a centrifugal switch in a well known manner. The centrifugal switch is effective in making and breaking electrical contacts for effecting a changeover in winding connections. Protection of motor switch contacts is important when motors are operated in areas where contacts may be subject to dust and dirt and any other foreign substances which may be detrimental to the operation of the starting switch. Any restrictions or hindrance to movement for making and breaking engagement of electrical contacts can result in delay or continued completion of circuit connections and can interfere with starting and running of a motor to the end that a main winding of a motor will burn out and require costly repair or replacement.

The improvement of the present invention provides for increased contact reliability due to isolation of switch contacts from dirt, oil, dust, grease and foreign substances such as carried by circulating air currents Within a motor frame or housing. In accordance with the improvement of the present invention, the switch mechanism 14 is provided with a shielding structure generally indicated by numeral 16. The shielding structure includes a cup-shaped member 160 having a central aperture through which a stem of movable contact 14m is inserted and extends through a hole 14k in intermediate portion of the resilient arm 14a. The stem is swaged or peened over at its free end to form a rivet-like portion 141- as seen in FIGURES 4 and 4a. This rivet-like portion Mr is adapted to engage a fixed abutment stop means, or end 16s having a curved surface and integral with an extension 16e of a web 16w secured to or integral with the U-shaped member 141:. Preferably the web 16w and extension lee form an integral part extending laterally relative to the U-shaped member 14a on a side thereof opposite to the side from which the projection 14;; protrudes.

In accordance with the present invention, the movable contact 14m provides a contact head portion that holds the cup-shaped member 16c securely in position relative to an intermediate portion of the resilient arm 14a. T he cupssh'aped member 160 includes an axially extending flange portion 16 which is concentric and coaxial relative to the movable contact 14m and the path of movement thereof. The shielding structure in accordance with the present invention further includes a grommet of elastomeric material having a first annular end portion 16x and a second annular end portion 163 The diameter of the first end portion 16x is greater than the diameter of the second end portion 16y. The end portions 16x and 16y are joined together by a laterally extending intermediate portion 16: that establishes coaxial alignment and longitudinal spacing of the end portions 162: and 16y relative to each other. The intermediate portion 161' can be deflected and flexes axially in between the end portions to permit limited telescoping of the end portions relative to each other under compressive force due to movement of the resilient arm 14a in response to shifting of sleeve 12s along the shaft S to the right as illustrated in FIG URE 4a. The intermediate portion 161' normally has a position as shown in FIGURE 4 such that the end portions are not in telescoping relation to each other and the resilience of the elastomeric material is such that the grommet exerts a ibasing force to maintain the fixed contact in a peripherally sealed relation as established by an inner seal surface 162 which is annular and complementary to peripheral outer surfaces of the fixed contact 140 and spacing means or washer 14w. Simultaneously with establishment of sealing engagement of the surface 16z relative to the fixed contact 140, the first end portion 16x is biased due to flexing of intermediate portion 16i for sealingly engaging an inner peripheral surface of the annular flange 16 of the cup-shaped member 16c. It is to be understood that the grommet is hollow and open at opposite ends adjacent to end portions 161' and 16y and the grommet per se provides no cavities or spaces in which air can be trapped so as to hinder or deter opening and closing of the contacts relative to each other. The extension 16e providing the stop means 16s is positioned so that the rivet-like portion 14r engages the stop 16s and maintains a predetermined spacing between the movable contact 1411: and fixed contact 140 such that the grommet is resiliently maintained intermediate the cup-shaped member 16c on arm 16a and the support 1417. Due to scaling engagement of opposite end portions relative tothe support 1412 and fixed contact 14:. as well as the cup-shaped member 16c, the contacts are kept protected and isolated from foreign substances and are relatively free of risk of oxidation because atmosphere is restricted and nearly excluded for minimizing any damage due to arcing and sparks relative to the contacts that are maintained at clean and fully operative condition for a long and indefinite period of time. Components of shielding structure are free of cement and limited breathing can occur adjacent to junctures though foreign material is restricted against passage relative to the contacts. Since the stop 16s maintains predetermined spacing of the contacts, positive fastening means such as cement are eliminated relative to the grommet. The grommet is free of slots or slits and is always in a location intermediate the contacts such that the arm 16a does not frictionally engage and foul contact opening and closing. The grommet can be made of any suitable elastomeric material such as silicone rubber, for example.

While the embodiments of the present invention constitue preferred forms, it is to be understood that other forms can be adopted.

What is claimed is as follows:

1. A switch contact assembly, consisting only of, a support of insulating material, a first contact fixed to said support, a resilient arrn fulcrumed at one end relative to said support, a second contact carried by said arm, a cupshaped cover member of rigid material concentric relative to said second contact and movable therewith, and

only a single annular grommet exclusively of elastomeric material having axially separated circular openings at opposite ends formed by a first axial relatively larger end portion and a second axial smaller end portion joined to each other at a location intermediate the openings by a laterally extending intermediate portion radially transverse to both said first as well as said second axial end portions and that establishes coaxial alignment and longitudinal spacing of the end portions, that permits limited direct axial telescoping of end portions relative to each other while flexed axially in between the end portions into a substantially Z-shape so as to bias end portions into sealing engagement inside said cover member and pe- I ripherally outside said fixed first contact, and that is maintained under compressive pressure at all times intermediate the contacts for elimination of friction though more freely deformable axially due to said Z-shape definitely faciliating opening and closing of contacts which are kept protected and isolated from foreign substances such as dirt, oil, dust and grease carried by circulating air currents.

2. On a switch contact assembly having a support of insulating material on which a first contact is fixedly attached and having a resilient arm fulcrumed at one end relative to the support as well as having a second contact carried by the resilient arm, the improvement which comprises having only a cup-shaped cover member of rigid material concentrically attached relative to said second contact on the resilient arm and only a single annular grommet exclusively of elastomeric material having axially aligned though separated circular openings at opposite ends formed by a first axial relatively larger end portion and a second axial smaller end portion joined to each other at a location intermediate the openings by a laterally extending intermediate portion normally radially transverse to both said larger and smaller end portions though adapted to permit limited concentric telescoping of said smaller and larger end portions relative to each other while flexed axially in between said end portions into a substantially Z-shape wherein said intermediate portion is acutely angular integrally in relation to said larger and smaller end portions so as to bias said end portions into sealing engagement inside said cover member and peripherally outside the fixed first contact, said single grommet having a predetermined axially compressive pressure thereon at all times intermediate the contacts due only to resilient urging of said intermediate portion to return to the normally radial condition thereof completely free of separate springing while said smaller and larger end portions engage one contact peripherally and said cover member respectively, said end portions and intermediate portion being integral though axially spaced with respect to each other.

3. In a dynamoelectric machine switching shield structure including a support of insulating material that carries a fixed metal contact as well as an arm movably mounted on the support with further contact means located concentrically within an annular cup-like cover member together carried by a free end of the arm and movable therewith in a path to permit making and breaking of electrical engagement relative to the fixed contact, the specific combination therewith of both a stop member located adjacent to the arm and extending from said support adjacent to where the arm is mounted therewith as well as only a single grommet means exclusively of elastomeric material having opposite annular openings axially separated from each other as formed by a relatively larger end portion and a smaller end portion with edges sealingly engageable peripherally outside said fixed contact and the movable contact means, respectively, said grommet means having a position resiliently maintained for sealing engagement at opposite end portions due to limit of movement effected by said stop member relative to the arm whereby said grommet means is maintained under compression axially at all times between the smaller and larger end portions, said end portions of said grommet purposely having differing diameters and being joined integrally by a laterally extending intermediate portion radially transverse to both the larger and smaller end portions and that establishes radial interconnection between end portions, that is effective axially in flexing into a substantially Z-shape to facilitate telescoping though enhancing biasing end portions into sealing engagement peripherally relative to the contact and contact means due to resilient urging of said intermediate portion to return to a normally radial and lateral outward position transverse rather than acutely angular to said larger and smaller end portions, and that provides conjoint action to serve simultaneously as a seal as well as a spring for biasing the contact and contact means apart while said stop member adjacent to the arm limits separation of the contacts such that said grommet is maintained in assembled relation thereto free of any external and additional spring means though said grommet is more freely deformable axially due to said Z-shape which definitely facilitates opening and closing of contacts which are simultaneously effectively protected and isolated from foreign substances such as dirt, oil, dust and grease carried by circulating air currents.

References Cited in the file of this patent UNITED STATES PATENTS 2,662,143 Eckles Dec. 8, 1953 2,813,180 Hantack Nov. 12, 1957 2,925,479 Mar-asco Feb. 16, 1960 

